This invention relates to ventilation devices such as non-invasive positive pressure ventilation (NIPPV) and continuous positive airway pressure (CPAP) devices which function to supply a patient with a supply of clean breathable gas (usually air, with or without supplemental oxygen) at a prescribed pressure or pressures at appropriate times during the patient's breathing cycle. The specification discloses a method and apparatus for fault diagnosis in such devices.
An example of a suitable device in which the invention may be included is the AutoSet® T device (ResMed Ltd., Australia), which may be used for treating sleep disordered breathing, such as Obstructive Sleep Apnea (OSA), as described in U.S. Pat. No. 5,704,345 (Berthon-Jones).
A NIPPV or CPAP device typically includes a flow generator, an air filter, a mask, an air delivery conduit connecting the flow generator output to the mask, various sensors and a microprocessor-based controller. The flow generator may include a servo-controlled motor and an impeller. The sensors measure, among other things, motor speed, gas volumetric flow rate and pressure. The air delivery circuit is that portion of the device's airflow path comprising the air inlet, the filter, the flow generator, the conduit and the mask. The device may optionally include a humidifier in the air delivery circuit. The controller may include data storage means.
One problem compromising the effective operation of such devices is that with time, the air inlet filter may become dirty, increasing the filter's resistance to the flow of air. It is known to provide a warning light which is activated after a given number of hours of operation of the device, to indicate that the filter should be cleaned or replaced. Such an approach does not take into account the fact that the rate of accumulation of dirt on the filter will depend on the environment in which the device is used. It may also be found that the patient may continue to use the device despite the warning light and thereby receive inadequate therapy. Importantly, the air delivery circuit may become partly or completely blocked for other reasons, without a warning being given.